The present invention relates to methods for producing integrated circuit devices and more specifically to a method for forming a bipolar emitter using doped spin on glass (SOG).
Known methods for forming emitters in bipolar complimentary metal oxide semiconductor (BiCMOS) devices involve a masking operation followed by an implant operation in which n-type and p-type impurities are implanted into a substrate, typically silicon. In such a process, the implant energy has to be reduced to produce shallow junctions.
This method suffers from the disadvantage that implanting produces defects which lie in the space charge region of the junction. The implanted impurity is brought to rest by an inelastic collision with silicon atoms in the crystal lattice, which damages the crystal lattice structure by knocking silicon atoms out of place. The crystal lattice structure must be epitaxially regrown by a thermal anneal to activate the implanted impurities by incorporating them into the crystal lattice. For shallow junctions, a rapid thermal process (RTP) cycle is typically done. However, the damage from implanting is not totally repairable without causing undesirable enhanced diffusion of the impurity which is inconsistent with shallow junction technology. Defect sites having energies in the middle of the band gap remain and produce a conduction path which ultimately causes a leakage current to flow.
Another known method for forming bipolar emitters includes the steps of depositing a layer of undoped polysilicon, masking off predetermined areas on the polysilicon, doping the unmasked areas of polysilicon with boron or phosphorus species, and heating the polysilicon to drive the species out of the polysilicon.
This method suffers from the disadvantage that the species are limited to boron and phosphorus and the resistance of the polysilicon line is quite high.
Therefore, it would be desirable to provide a process for forming a low-resistance bipolar emitter with a shallow junction, which does not suffer from the disadvantages of known process steps.